This invention relates generally to ion beam apparatus, and, more particularly, relates to apparatus and methods for selectively deflecting and blanking an ion beam.
Ion beam devices employed for mask repair and other applications typically include elements for blanking the ion beam when the ion beam is not to impinge on the workpiece. Examples of such configurations are discussed in the following U.S. Pat. Nos.:
______________________________________ 4,820,928 Ooyama et al. 4,661,702 Welkie 4,649,316 Cleaver et al. 4,503,329 Yamaguchi et al. 4,439,685 Plies ______________________________________
Beam blanking apparatus is also disclosed in the following Japanese patent publications:
1-176,082 PA0 64-089,254 PA0 62-229,645 PA0 62-177,849 PA0 62-103,950 PA0 60-089,051 PA0 60-074,249 PA0 59-116,600
In particular, the Ooyama et al. patent discloses particle beam lithography apparatus in which the beam scans a target region of the sample to draw a pattern. The apparatus selectively blanks the beam to ensure that the beam impinges upon the sample only within the selected target region.
The Welkie patent discloses a SIMS apparatus having ion beam blanking. An ion gun scans an area of the workpiece surface to sputter etch a crater. After the crater is formed, a beam blanking element limits the ion beam to etch a second, smaller crater at the bottom of the first crater, so that the ion beam does not hit the side wall of the first crater. This reduces errors introduced into the SIMS measurement from material from the side wall of the first crater.
The Cleaver et al. patent discloses an ion beam blanker system having four magnets arranged on an optical axis. Between the two center magnets is a blanking plate having an off-axis aperture. When the magnets are energized, the ion beam is deflected by an amount depending upon the charge/mass ratio of the ion species in the beam. By deflecting the beam such that the focal point is displaced away from the aperture, the ion beam is blanked off.
The Yamaguchi et al. patent discloses a scanning ion beam apparatus having a controlled beam blanking electrode for limiting the region of the workpiece subject to sputtering by the ion beam.
Plies discloses a beam blanking system having a three electrode Einzel filter lens employed as a blanking lens. The center electrode, which is at high voltage, has a blanking signal applied to it via a capacitor. The blanking lens is inserted in the beam path such that its object side nodal point coincides with the virtual source image. The beam is blocked by utilizing a sufficiently negative auxiliary voltage at the center electrode, and a pinhole diaphragm positioned downstream from the blanking lens.
Japanese Patent No. 62-229,645 discloses focused ion beam apparatus for ion implantation. The apparatus includes two-stage blanking plates having the same gain, arranged between two lenses.
Japanese Patent No. 60-089,051 discloses an ion beam device having beam blanking electrodes disposed symmetrically within a Wien filter along the axis of propagation.
Japanese Patent No. 60-074,249 discloses an ion beam device having filters arranged along the beam axis in two stages, with a beam blanking electrode disposed between filters.
Japanese Patents 1-176,082, 64-089,254, 62-177,849, 62-103,950, and 59-116,600 also disclose beam blanking devices.
Additionally, a publication by G. Ryding of Eaton Corporation discusses dose control for ion implantation apparatus, and discloses Faraday designs incorporating electrostatic or magnetic suppression of secondary particles.
Conventional beam blanking designs, however, suffer from a number of deficiencies that reduce their utility. One such limitation is ion beam instability due to hydrocarbon cracking, hydrocarbon buildup, and consequent accumulation of charge on beam blanking deflection plates. This instability reduces the ability to maintain precise control of ion beam position.
Beam blanking systems typical of the prior art also lack provision for simple, rapid and accurate measurement of ion beam current.
It is accordingly an object of the invention to provide improved beam blanking methods and apparatus.
Another object of the invention is to provide beam blanking methods and apparatus that facilitate precise control of ion beam position.
It is a further object of the invention to provide beam blanking methods and apparatus that enable accurate measurement of ion beam current.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.